In the US alone, over 1,000,000 procedures to insert pressure equalizing tubes (PETs) in the tympanic membrane (TM) are performed each year. These tubes allow fluid from middle ear infections to drain from the middle ear to the external ear canal, thus relieving the pain from pressure build-up. Chronic TM perforations are generally thought to occur when PETs are left in the TM for extended periods of time. For PETs left in the TM for 18 months or less, the chronic TM perforation rate is between 1-5%. However, some patients require PETs for 2 years or longer—the rate of chronic TM perforation for this group is about 9%.
To treat chronic TM perforations, the fibrous tissue around the perforation is abraded to induce an inflammatory response. If the perforation is small such as about 20% or less of the cross-sectional area of the TM, the perforation can be packed with either paper or fat taken from the earlobe. Larger perforations require a more substantial packing material, such as autografts of cartilage or fascia, surgical gelatin, or a synthetic polymer patch. All of these therapies require some kind of surgery, and the success rate of the therapy is highly dependent upon the skill of the surgeon.
There are several commercial otologic packing products available in the market. Pfizer manufactures Gelfoam®, a type of surgical gelatin obtained from pigs used as a packing material for the middle ear after surgery. Typically, once the middle ear has been cleared of fluid via surgery, Gelfoam® is used to fill the void in the middle ear. Gelfoam® liquefies when hydrated, and is degraded and cleared easily by the body. In addition to acting as a barrier between the middle and external ear while the TM perforation heals, it also provides a surface to which autografts or patches may adhere. However, due to the nature of porcine gelatin, some patients may be allergic to this material.
Medtronic ENT/Xomed manufactures Merogel®, a fibrous packing material similar to that of Gelfoam®, but is instead made of hyaluronic acid. Merogel® turns into a gel when hydrated, and is easily degraded. It has the same properties as Gelfoam®, but without the risk of allergic reaction due to porcine gelatin. Like Gelfoam®, it is used to pack the middle ear prior to insertion of an autograft or patch, and is not used as a stand-alone treatment.
Medtronic ENT/Xomed also manufactures EpiDisc™, a porous hyaluronic patch intended to repair tympanic membranes. It is biodegradable and induces both epithelial cell growth and vascular in-growth of the tympanic membrane. However, to use this patch, it must be trimmed to the size of the perforation and inserted surgically. Occasionally, the patch fails to adhere completely to the native tissue or packing material in the middle ear, resulting in additional surgery to replace the patch.
None of the current products available for repairing TM-perforation deliver drugs directly to the middle ear. The current method for delivering drugs directly to the middle ear is with eardrops. The main drug used for treating ear infections (ciprodex) stings when applied. This is an important factor to consider when the majority of the patients treated for ear infections are children under the age of 10.
To date, no photopolymerizable hydrogels have been used as scaffolds for otologic use, in which the liquid polymer is applied to the desired site prior to curing. Blue light-polymerizable materials are used in the dental field, but none of the components apply to otologic use. Using a scaffold that is initially a liquid and only forms a scaffold upon exposure to specific conditions is a total departure from current and traditional therapies for repairing TM perforations.
While certain novel features of this invention shown and described below are pointed out in the claims, the invention is not intended to be limited to the details specified, since a person of ordinary skill in the relevant art will understand that various omissions, modifications, substitutions and changes in the forms and details of the invention illustrated and in its operation may be made without departing in any way from the spirit of the present invention. No feature of the invention is critical or essential unless it is expressly stated as being “critical” or “essential.”